A married couple with three kids is getting divorced, so that one of them can marry their live-in girlfriend and keep the trio happily intact.

Polygamous couple Cristina and Benno Kaiser have been married for 12 years, but have decided to call it quits on paper so their 21-year-old lover, Sierra Kuntz, knows how committed they are to her, and sticks with them through thick and thin, the couple said in an interview with Barcoft Media.

The new marriage will give Kuntz legal rights to the Kaisers' three kids, ages 6, 7 and 11.

"Cristina and I decided this was something that needed to be done in order for Sierra to understand the depth of how much we love her and want her to be part of our family," Benno told the news outlet.

"The benefits of one of us marrying her are going to be on many different levels," he said.

A married couple with three kids is getting divorced, so that one of them can marry their live-in girlfriend and keep the trio happily intact.

Benno, a legal assistant, added, "She is going to be legally considered a parent to the children and, more importantly, it will show her that this is not a temporary thing, we both love her and it's something that's meant to be permanent."

Cristina, 31, and Benno, 37, met 12 years ago while they both were serving in the US Military Police Corps in Virginia.

At some point in the marriage, Cristina, also a legal assistant, began to feel something was missing.

"Initially, it was my idea to open the marriage. I brought it to Benno's attention and told him I would like to introduce women to our relationship to see where it goes," said Cristina, who met Kuntz while shopping in Las Vegas.

"At first I was very hesitant about getting involved with a married couple," Kuntz said.

"I was worried that I would be disposable and that this was a phase they were going through. But when I spent time with them, I realized what they wanted and feel this was a situation I could work with, so I jumped on board," said Kuntz.

The couple said they're still deciding which one will tie the knot with Kuntz.

Benno said their children are aware of the unique marital dynamic.

"We had talked to our children before this and let them know we wanted to adopt someone and bring somebody into our relationship. Our children have been very supportive of this. They have understood," he said.